Sputtering target for forming high-resistance transparent conductive film, and method for producing the film

ABSTRACT

The present invention provides an ITO sputtering target for forming a high-resistance transparent conductive film which target can be used virtually in a DC magnetron sputtering apparatus and can form a high-resistance, transparent film, and a method for producing a high-resistance transparent conductive film. The sputtering target for forming a high-resistance transparent conductive film having a resistivity of about (0.8-10)×10 −3  Ωcm contains indium oxide, an insulating oxide, and optionally tin oxide.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to a sputtering target for use inproduction of a high-resistance transparent conductive film having aresistivity of about (0.8-10)×10⁻³ Ωcm, and to a method for producing ahigh-resistance transparent conductive film from the sputtering target.

[0003] 2. Background Art

[0004] Indium oxide-tin oxide (In₂O₃—SnO₂ complex oxide, hereinafterreferred to as “ITO”) film, which is a transparent conductive filmhaving high visible light transparency and high electrical conductivity,finds a variety of uses including heat-generating film for preventingdew formation on liquid crystal displays or glass plates, and infraredbeam-reflecting film.

[0005] When transparent conductive film is used in a flat panel display(FPD), a low-resistivity transparent conductive film having aresistivity of about 2×10⁻⁴ Ωcm is employed.

[0006] Meanwhile, a transparent conductive film employed as a resistancetouch panel attached to displays such as the above FPD is required toexhibit high-resistance characteristics (e.g., sheet resistance of about700 to 1,000 Ω) on the basis of the operation mechanism of the touchpanel.

[0007] However, in order for an ITO film conventionally employed in FPDsto be used as a transparent conductive film for a touch panel, thethickness of the conductive film must be reduced considerably, raising aproblem that sufficient touch panel strength fails to be ensured.

[0008] Also, when the resistance of an ITO sputtering target itself isincreased, a DC magnetron sputtering apparatus, which is inexpensive ascompared with a high-frequency magnetron sputtering apparatus, cannot beemployed. Thus, facility cost increases enormously, raising anotherproblem.

SUMMARY OF THE INVENTION

[0009] In view of the foregoing, the present invention has beenaccomplished in order to solve the aforementioned problem. Thus, anobject of the present invention is to provide an ITO sputtering targetfor forming a high-resistance transparent conductive film which targetcan be used virtually in a DC magnetron sputtering apparatus and canform a high-resistance, transparent film. Another object of theinvention is to provide a method for producing a high-resistancetransparent conductive film.

[0010] Accordingly, in a first mode of the present invention for solvingthe aforementioned problems, there is provided a sputtering target forforming a high-resistance transparent conductive ITO film having aresistivity of about (0.8-10)×10⁻³ Ωcm, the target comprising indiumoxide, an insulating oxide, and optionally tin oxide, According to firstmode, addition of the insulating oxide to the ITO sputtering targetincreases the resistivity of the formed transparent conductive filmwithout greatly modifying the resistivity of the target itself.

[0011] In a second mode of the present invention, the insulating oxidementioned in relation to the first mode is at least one species selectedfrom the group consisting of silicon oxide, aluminum oxide, tantalumoxide, hafnium oxide, niobium oxide, yttrium oxide, cerium oxide,praseodymium oxide, beryllium oxide, magnesium oxide, calcium oxide,strontium oxide, barium oxide, scandium oxide, titanium oxide, zirconiumoxide, vanadium oxide, boron oxide, gallium oxide, zinc oxide, chromiumoxide, manganese oxide, iron oxide, molybdenum oxide, phosphorus oxide,and lanthanoid oxides.

[0012] According to the second mode, addition of an oxide such assilicon oxide, aluminum oxide, tantalum oxide, niobium oxide, yttriumoxide, cerium oxide, or praseodymium oxide to the sputtering targetincreases the resistivity of the formed transparent conductive filmwithout greatly modifying the resistivity of the target itself.

[0013] In a third mode of the present invention, the insulating oxidementioned in relation to the second mode is silicon oxide.

[0014] According to the third mode, addition of silicon oxide to thesputtering target increases the resistivity of the formed transparentconductive film without greatly modifying the resistivity of the targetitself.

[0015] In a fourth mode of the present invention, the sputtering targetmentioned in relation to any one of the first to third modes contains anamount of an element which forms the aforementioned insulating oxidewith oxygen, the amount being 0.00001 to 0.26 mol based on 1 mol ofindium.

[0016] According to the fourth mode, addition of a predetermined amountof insulating oxide to the sputtering target increases the resistivityof the formed transparent conductive film without greatly modifying theresistivity of the target itself.

[0017] In a fifth mode of the present invention, the sputtering targetmentioned in relation to any one of the first to fourth modes containstin (Sn) in an amount of 0 to 0.3 mol based on 1 mol of indium.

[0018] According to the fifth mode, a sputtering target containingpredominantly indium oxide and optionally tin oxide is obtained.

[0019] In a sixth mode of the present invention, the sputtering targetmentioned in relation to any one of the first to fifth modes issubjected to DC magnetron sputtering, to thereby form a transparentconductive film having a resistivity of (0.8-10)×10⁻³ Ωcm.

[0020] According to the six mode, a high-resistivity transparentconductive film can be produced through DC magnetron sputtering.

[0021] A seventh mode of the present invention provides a method forproducing a high-resistance transparent conductive film, comprisingforming a transparent conductive film having a resistivity of(0.8-10)×10⁻³ Ωcm through DC magnetron sputtering from a sputteringtarget containing indium oxide, an insulating oxide, and optionally tinoxide.

[0022] According to the seventh mode, a sputtering target containing aninsulating oxide is used. Thus, a transparent conductive film having aresistivity of (0.8-10)×10⁻³ Ωcm can be formed through DC magnetronsputtering without greatly modifying the resistivity of the targetitself.

[0023] In an eighth mode of the present invention, the insulating oxidementioned in relation to the seventh mode is at least one speciesselected from the group consisting of silicon oxide, aluminum oxide,tantalum oxide, hafnium oxide, niobium oxide, yttrium oxide, ceriumoxide, praseodymium oxide, beryllium oxide, magnesium oxide, calciumoxide, strontium oxide, barium oxide, scandium oxide, titanium oxide,zirconium oxide, vanadium oxide, boron oxide, gallium oxide, zinc oxide,chromium oxide, manganese oxide, iron oxide, molybdenum oxide,phosphorus oxide, and lanthanoid oxides.

[0024] According to the eighth mode, a sputtering target containing anoxide such as silicon oxide, aluminum oxide, tantalum oxide, niobiumoxide, yttrium oxide, cerium oxide, or praseodymium oxide is used. Thus,a transparent conductive film having a resistivity of (0.8-10)×10⁻³ Ωcmcan be formed through DC magnetron sputtering without greatly modifyingthe resistivity of the target itself.

[0025] In a ninth mode of the present invention, the insulating oxidementioned in relation to the eighth mode is silicon oxide.

[0026] According to the ninth mode, a sputtering target containingsilicon oxide is used. Thus, a transparent conductive film having aresistivity of (0.8-10)×10⁻³ Ωcm can be formed through DC magnetronsputtering without greatly modifying the resistivity of the targetitself.

[0027] In a tenth mode of the present invention, the sputtering targetmentioned in relation to any one of the seventh to ninth modes containsan amount of an element which forms the aforementioned insulating oxidewith oxygen, the amount being 0.00001 to 0.26 mol based on 1 mol ofindium.

[0028] According to the tenth mode, a sputtering target containing apredetermined amount of insulating oxide is used, Thus, a transparentconductive film having a resistivity of (0.8-10)×10⁻³ Ωcm can be formedthrough DC magnetron sputtering without greatly modifying theresistivity of the target itself.

[0029] In an eleventh mode of the present invention, the sputteringtarget mentioned in relation to any one of the seventh to tenth modescontains tin (Sn) in an amount of 0 to 0.3 mol based on 1 mol of indium.

[0030] According to the eleventh mode, a sputtering target containingpredominantly indium oxide and optionally tin oxide is used. Thus, atransparent conductive film having a resistivity of (0.8-10)×10⁻³ Ωcmcan be formed through DC magnetron sputtering without greatly modifyingthe resistivity of the target itself.

BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Various other objects, features, and many of the attendantadvantages of the present invention will be readily appreciated as thesame becomes better understood with reference to the following detaileddescription of the preferred embodiments when considered in connectionwith accompanying drawings, in which:

[0032]FIG. 1 is a graph showing the relationship between partial oxygenpressure and resistivity and the relationship between partial oxygenpressure and transmittance (at a wavelength of 550 nm) of transparentconductive film produced in Example 1;

[0033]FIG. 2 is a graph showing the relationship between partial oxygenpressure and resistivity and the relationship between partial oxygenpressure and transmittance (at a wavelength of 550 nm) of transparentconductive film produced in Comparative Example 1; and

[0034]FIG. 3 is a graph showing the relationship between partial oxygenpressure and resistivity and the relationship between partial oxygenpressure transmittance (at a wavelength of 550 nm) of transparentconductive film produced in Example 2.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

[0035] The sputtering target for forming a high-resistancetransparent-conductive film according to the present invention is asintered oxide which contains indium oxide as a predominant component,tin oxide as an optional component, and an insulating oxide as anadditive. No particular limitation is imposed on the form of thecomponent oxides, and the oxides may assume individual oxides, complexoxides thereof, or solid solution thereof.

[0036] Examples of the insulating oxide include silicon oxide, aluminumoxide, tantalum oxide, hafnium oxide, niobium oxide, yttrium oxide,cerium oxide, praseodymium oxide, beryllium oxide, magnesium oxide,calcium oxide, strontium oxide, barium oxide, scandium oxide, titaniumoxide, zirconium oxide, vanadium oxide, boron oxide, gallium oxide, zincoxide, chromium oxide, manganese oxide, iron oxide, molybdenum oxide,phosphorus oxide, and lanthanoid oxides.

[0037] The insulating oxide preferably has a standard energy offormation lower than that of indium oxide within a temperature rangeabout 0 to about 1,600° C. This is because such an insulating oxide ischemically more stable than indium oxide and difficult to decompose.

[0038] The insulating oxide content (amount of the element(s) whichform(s) the aforementioned insulating oxide with oxygen) preferablyfalls within a range of 0.00001 to 0.26 mol based on 1 mol of indium.This is because when the insulating oxide content is less than the lowerlimit, the effect of addition is no longer prominent, whereas when thecontent is in excess of the upper limit, the resistance of the formedtransparent conductive film is excessively high.

[0039] In the present invention, the tin (Sn) content falls within arange of 0 to 0.3 mol based on 1 mol of indium. When tin is incorporatedinto the sputtering target, the tin (Sn) content falls within a range of0.001 to 0.3 mol, preferably 0.01 to 0.15 mol, more preferably 0.05 to0.1 mol based on 1 mol of indium. When the tin content falls within theabove ranges, density and mobility of carriers (electrons) present inthe sputtering target can be appropriately controlled, therebymaintaining electrical conductivity within an appropriate range. Incontrast, when the tin content falls outside the above ranges, mobilityof carriers present in the sputtering target decreases and conductivitydeteriorates, which is not preferred.

[0040] The sputtering target for forming a high-resistance transparentconductive film of the present invention has such a low resistivity asto permit DC magnetron sputtering of the target. However, from thesputtering target, a high-resistance transparent conductive film havinga resistivity of (0.8-10)×10⁻³ Ωcm can be formed.

[0041] Needless to say, a high-frequency magnetron sputtering apparatusmay also be employed, to thereby form a high-resistance transparentconductive film having a resistivity of (0.8-10)×10⁻³ Ωcm.

[0042] The method for producing the sputtering target of the presentinvention will next be described with reference to some exemplary steps,which should not be construed as limiting the production method thereto.

[0043] Generally employed starting materials for forming the sputteringtarget of the present invention include In₂O₃, SnO₂, SiO₂ powders.Instead of these oxides, the corresponding elements, compounds, complexoxides, etc. may be employed as starting materials. Prior to use asstarting materials, the elements and compounds are subjected to aprocess for transforming into the corresponding oxides.

[0044] No particular limitation is imposed on the methods of mixing theraw material powders in desired proportions and of compacting themixture. The resultant mixture is compacted through any ofconventionally known wet methods and dry methods.

[0045] Examples of the dry methods include the cold press method and thehot press method. According to the cold press method, a powder mixtureis charged into a mold and pressed so as to form a compact, and theresultant compact is fired and sintered in air or an oxygen-containingatmosphere. According to the hot press method, a powder mixture placedin a mold is sintered with pressing.

[0046] Examples of preferred wet methods include a filtration moldingmethod (disclosed in Japanese Patent Application Laid-Open (kokai) No.11-286002). The filtration molding method employs a filtration mold,formed of a water-insoluble material, for removing water under reducedpressure from a ceramic raw material slurry, to thereby yield a compact,the filtration mold comprising a lower mold having one or morewater-discharge holes; a water-passing filter for placement on the lowermold; a seal material for sealing the filter; and a mold frame forsecuring the filter from the upper side through intervention of the sealmaterial. The lower mold, mold frame, seal material, and filter, whichcan be separated from one another, are assembled to thereby form thefiltration mold. According to the filtration molding method, water isremoved under reduced pressure from the slurry only from the filterside. In a specific operation making use of the filtration mold, aceramic powder mixture, ion-exchange water, and an organic additive aremixed, to thereby prepare a slurry, and the slurry is poured into thefiltration mold. Water contained in the slurry is removed under reducedpressure from only the filter side, a compact is yielded. The resultantceramic compact is dried, debindered, and fired.

[0047] In the aforementioned methods, the firing temperature ispreferably 1,300 to 1,600° C., more preferably 1,300 to 1,450° C. Afterfiring, the fired compact is mechanically worked so as to form a targethaving predetermined dimensions,

EXAMPLES

[0048] The present invention will next be described in detail by way ofexamples, which should not be construed as limiting the inventionthereto.

Example 1

[0049] In₂O₃ powder (purity: >99.99%), SnO₂ powder (purity: >99.99%),and SiO₂ powder (purity: >99.9%) were mixed in proportions of 85 wt. %,10 wt. %, and 5 wt. % (Si: about 0.13 mol based on 1 mol of In),respectively, to thereby yield a powder mixture (approximately 1.5 kg).The mixture was compacted through filtration molding, to thereby preparea compact. The compact was fired in an oxygen-containing atmosphere at1,550° C. for 8 hours, to thereby yield a sintered compact. The sinteredcompact was subjected to a working step, to thereby yield a targethaving a relative density of 100% based on the theoretical density. Thetarget was found to have a bulk resistivity of 2.4×10⁻⁴ Ωcm.

[0050] The target was subjected to DC magnetron sputtering under thefollowing conditions, whereby an oxide film having a thickness of 1,200Å was formed.

[0051] Sputtering Conditions:

[0052] Target dimensions: φ=6 inches, t=6 mm

[0053] Mode of sputtering: DC magnetron sputtering

[0054] Evacuation apparatus: Rotary pump+cryo-pump

[0055] Vacuum attained: 4.0×10⁻⁶ [Torr]

[0056] Ar pressure: 3.0×10⁻³ [Torr]

[0057] Oxygen pressure: 1×10⁻⁵ to 10×10⁻⁵ [Torr]

[0058] Substrate temperature: 200° C.

[0059] Electric power for sputtering: 300 W (power density: 1.6 W/cm²)

[0060] Substrate used: TEMPAX (glass sheet for liquid crystal display, t1.8 mm)

[0061] Through analysis of the film in terms of resistivity andtransmittance, the relationship between partial oxygen pressure andresistivity and the relationship between partial oxygen pressure andtransmittance (at a wavelength of 550 nm) were obtained. The results areshown in FIG. 1.

Comparative Example 1

[0062] In₂O₃ powder (purity: >99.99%) and SnO₂ powder (purity: >99.99%)were mixed in proportions of 90 wt. % and 10 wt. %, respectively, tothereby yield a powder mixture (approximately 1.5 kg). The mixture wascompacted through filtration molding, to thereby prepare a compact. Thecompact was fired in an oxygen-containing atmosphere at 1,550° C. for 8hours, to thereby yield a sintered compact. The sintered compact wassubjected to a working step, to thereby yield a target having a relativedensity of 99.6% based on the theoretical density. The target was foundto have a bulk resistivity of 1.7×10⁻⁴ Ωcm.

[0063] The target was subjected to DC magnetron sputtering under theconditions as employed in Example 1, whereby an oxide film having athickness of 2,000 Å was formed. Through analysis of the film in termsof resistivity and transmittance, the relationship between partialoxygen pressure and resistivity and the relationship between partialoxygen pressure and transmittance (at a wavelength of 550 nm) wereobtained. The results are shown in FIG. 2.

Example 2

[0064] In₂O₃ powder (purity: >99.99%), SnO₂ powder (purity: >99.99%),and SiO₂ powder (purity: >99.9%) were mixed in proportions of 80 wt. %,10 wt. %, and 10 wt. % (Si: about 0.26 mol based on 1 mol of In),respectively, to thereby yield a powder mixture (approximately 1.5 kg).The mixture was compacted through filtration molding, to thereby preparea compact. The compact was fired in an oxygen-containing atmosphere at1,550° C. for 8 hours, to thereby yield a sintered compact. The sinteredcompact was subjected to a working step, to thereby yield a targethaving a relative density of 100% based on the theoretical density. Thetarget was found to have a bulk resistivity of 4.0×10⁻⁴ Ωcm.

[0065] The target was subjected to DC magnetron sputtering under theconditions as employed in Example 1, whereby an oxide film having athickness of 1,200 Å was formed. Through analysis of the film in termsof resistivity and transmittance, the relationship between partialoxygen pressure and resistivity and the relationship between partialoxygen pressure and transmittance (at a wavelength of 550 nm) wereobtained. The results are shown in FIG. 3.

Example 3

[0066] In₂O₃ powder (purity: >99.99%), SnO₂ powder (purity: >99.99%),and SiO₂ powder (purity: >99.9%) were mixed in proportions of 85 wt. %,10 wt. %, and 5 wt. % (Si: about 0.13 mol based on 1 mol of In),respectively, to thereby yield a powder mixture (approximately 1.5 kg).The mixture was compacted through filtration molding, to thereby preparea compact. The compact was fired in an oxygen-containing atmosphere at1,450° C. for 8 hours, to thereby yield a sintered compact. The sinteredcompact was subjected to a working step, to thereby yield a targethaving a relative density of 100% based on the theoretical density. Thetarget was found to have a bulk resistivity of 3.0×10⁻⁴ Ωcm.

[0067] The target was subjected to DC magnetron sputtering under theconditions as employed in Example 1, whereby an oxide film having athickness of 1,200 Å was formed. Through analysis of the film, variationprofiles of resistivity and transmittance with respect to partial oxygenpressure were found to be similar to those shown in FIG. 1.

[0068] As described above, the sputtering targets produced in Examples 1to 3 had a bulk resistivity on the level of some 10⁻⁴ Ωcm, which isalmost equivalent to the bulk resistivity of the conventional ITO targetof Comparative Example 1. Such a low bulk resistivity indicates that thesputtering targets of the invention can be subjected to DC magnetronsputtering.

[0069] The film samples produced in Examples 1 to 3 exhibit variationprofiles of resistivity and transmittance with respect to partial oxygenpressure similar to those of the conventional ITO film produced inComparative Example 1. The similarity indicates that conventionalmethods for forming ITO film can also be employed for formingtransparent conductive film from the sputtering target of the presentinvention.

[0070] A resistivity at an optimum partial oxygen pressure of thetransparent conductive film of Example 1 is ten times that of theconventional ITO film produced in Comparative Example 1. Similarly, aresistivity at an optimum partial oxygen pressure of the transparentconductive film of Example 2 is one hundred times that of the ITO filmof Comparative Example 1.

[0071] If a commercial transparent conductive film having a thickness ofabout 150 Å is produced from the sputtering target of the presentinvention, sheet resistance of the film produced in accordance withExample 1 would be about 700 Ω, and that of the film produced inaccordance with Example 2 would be about 7,000 Ω. If a commercialtransparent conductive film having a thickness of 1,500 Å is produced,sheet resistance of the film produced in accordance with Example 1 wouldbe about 70 Ω, and that of the film produced in accordance with Example2 would be about 700 Ω.

[0072] As is already known, when the amount of SnO₂ added to thesputtering target increases, carrier formation is promoted, therebylowering the resistance thereof. Thus, in addition to controlling theamount of SiO₂, modification of the amount of SnO₂ can control theresistivity of the sputtering target.

[0073] Therefore, optimum resistivity of transparent conductive film canbe attained by controlling the amounts of SnO₂ and SiO₂,

[0074] As described hereinabove, the present invention provides asputtering target for forming a high-resistance transparent conductivefilm having a resistivity of about (0.8-10)×10⁻³ Ωcm, comprising indiumoxide, an insulating oxide, and optionally tin oxide. From thesputtering target, a high-resistance transparent conductive film can beformed virtually by means of a DC magnetron sputtering apparatus.

What is claimed is:
 1. A sputtering target for forming a high-resistancetransparent conductive ITO film having a resistivity of about(0.8-10)×10⁻³ Ωcm, the target comprising indium oxide, an insulatingoxide, and optionally tin oxide.
 2. A sputtering target for forming ahigh-resistance transparent conductive film according to claim 1,wherein the insulating oxide is at least one species selected from thegroup consisting of silicon oxide, aluminum oxide, tantalum oxide,hafnium oxide, niobium oxide, yttrium oxide, cerium oxide, praseodymiumoxide, beryllium oxide, magnesium oxide, calcium oxide, strontium oxide,barium oxide, scandium oxide, titanium oxide, zirconium oxide, vanadiumoxide, boron oxide, gallium oxide, zinc oxide, chromium oxide, manganeseoxide, iron oxide, molybdenum oxide, phosphorus oxide, and lanthanoidoxides.
 3. A sputtering target for forming a high-resistance transparentconductive film according to claim 2, wherein the insulating oxide issilicon oxide.
 4. A sputtering target for forming a high-resistancetransparent conductive film according to claim 1, wherein the sputteringtarget contains an amount of an element which forms the insulating oxidewith oxygen, the amount being 0.00001 to 0.26 mol based on 1 mol ofindium.
 5. A sputtering target for forming a high-resistance transparentconductive film according to claim 1, wherein the sputtering targetcontains tin (Sn) in an amount of 0 to 0.3 mol based on 1 mol of indium.6. A sputtering target for forming a high-resistance transparentconductive film according to claim 1, wherein the sputtering target issubjected to DC magnetron sputtering, to thereby form a transparentconductive film having a resistivity of (0.8-10)×10⁻³ Ωcm.
 7. A methodfor producing a high-resistance transparent conductive film, comprisingforming a transparent conductive film having a resistivity of(0.8-10)×10⁻³ Ωcm through DC magnetron sputtering from a sputteringtarget containing indium oxide, an insulating oxide, and optionally tinoxide.
 8. A method for producing a high-resistance transparentconductive film according to claim 7, wherein the insulating oxide is atleast one species selected from the group consisting of silicon oxide,aluminum oxide, tantalum oxide, hafnium oxide, niobium oxide, yttriumoxide, cerium oxide, praseodymium oxide, beryllium oxide, magnesiumoxide, calcium oxide, strontium oxide, barium oxide, scandium oxide,titanium oxide, zirconium oxide, vanadium oxide., boron oxide, galliumoxide, zinc oxide, chromium oxide, manganese oxide, iron oxide,molybdenum oxide, phosphorus oxide, and lanthanoid oxides.
 9. A methodfor producing a high-resistance transparent conductive film according toclaim 8, wherein the insulating oxide is silicon oxide.
 10. A method forproducing a high-resistance transparent conductive film according toclaim 7, wherein the sputtering target contains an amount of an elementwhich forms the aforementioned insulating oxide with oxygen, the amountbeing 0.00001 to 0.26 mol based on 1 mol of indium.
 11. A method forproducing a high-resistance transparent conductive film according toclaim 7, wherein the sputtering target contains tin (Sn) in an amount of0 to 0.3 mol based on 1 mol of indium.